Wildfires Send Tons of Mercury Up in Smoke

BOULDER, Colorado, August 27, 2001 (ENS) - The wildfires now burning across the Western United States are releasing tons of mercury into the atmosphere, say researchers from the National Center for Atmospheric Research. More than 21,700 firefighters and support personnel are now battling wildland fires burning on more than 200,000 acres in seven states.

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Mercury laden smoke from wildfires blows over suburban and urban areas (Photo courtesy National Interagency Fire Center)
During a wildfire, mercury stored in the foliage and ground litter is released and carried into the atmosphere, says Hans Friedli, a scientist from the National Center for Atmospheric Research (NCAR). He and colleague Lawrence Radke are conducting experiments in the laboratory as well as in research flights over wildfires and prescribed burns.

Scientists from NCAR and the University of Washington are currently flying over wildfires in the Pacific Northwest to measure mercury emissions in their smoke.

Scientists are trying to understand the global sources of atmospheric mercury, as well as how much ends up in the food chain after deposition on land and water. Friedli and Radke's research provides one more piece in the global inventory puzzle.

Gaseous elemental mercury in the atmosphere travels the globe for about a year before being deposited on land or water. About 6,500 tons, all well mixed, are circulating at any one time.

About half the atmospheric mercury got there from natural sources in soil, oceans and volcanoes, and the other half through human activity. The U.S. Environmental Protection Agency (EPA) estimates that 41 tons of mercury are released each year by coal fired plants in the U.S.

Mercury is transformed in the atmosphere through chemical processes and then rains or falls out as wet or dry deposition to the surface. For trees, "wet deposition is most important," said Friedli. "Mercury is picked up by the surfaces - the leaves or needles - and it stays there." At least until those trees burn.

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Hans Friedli will be measuring mercury emissions from fires in the Pacific Northwest this month (Photo by Carlye Calvin, courtesy NCAR)
Friedli and Radke conducted laboratory tests to find out how much mercury a fire could release. For the experiment, forest samples from across the continental U.S. were set alight at the U.S. Forest Service Fire Science Laboratory's burn facility in Missoula, Montana.

The team's sensors immediately detected mercury. All samples released almost all of the mercury they had stored - from 94 percent to 99 percent. All the samples contained mercury at levels ranging from 14 to 71 nanograms per gram of fuel. A nanogram is one trillionth of a gram; about 28 grams make an ounce.

The team extrapolated their findings to global biomass burning from wildfires and from human activities, such as clearing land for agriculture. They estimated the contribution at up to 800 tons per year, or 25 percent of all manmade sources of airborne mercury.

When the mercury enters the food chain, it can put wildlife and humans at risk. The highest levels of atmospheric mercury ever observed were reported this spring from the National Oceanic and Atmospheric Administration's Point Barrow Observatory in Alaska.

Native Arctic populations consuming the region's game and fish are thought to be at severe risk. Long range atmospheric transport brings the mercury to the Arctic, where chemical reactions tied to springtime ozone depletion lead to increased mercury deposits to the region's land and water.

The mercury studies grew out of Friedli and Radke's National Science Foundation sponsored research with colleagues at NCAR to understand and predict the erratic, deadly behavior of wildfires. To develop better forecasts of wildfire behavior for firefighters, the researchers are combining computer models with observations from infrared cameras.

Friedli and Radke will aim ground based sensors at a prescribed burn in Prince Albert National Park in Saskatchewan, Canada this September. Last summer, when the team flew over a wildfire in Quebec, the mercury emissions were higher than in the lab experiment, "presumably because mercury in real fires is also emitted from heated soil," explained Friedli, "a source not yet considered in our experiments."

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Mercury emissions from this boreal forest fire near Hearst, Ontario, last July were measured with instruments aboard a Twin Otter aircraft. Flights over wildfires are used to confirm Friedli and Radke's laboratory findings (Photo by Ian MacPherson, courtesy National Research Council of Canada)
This month, the team will overfly one or more of the large fires burning in the Pacific Northwest.

The National Interagency Fire Center said today that fire activity seems to be stabilizing across the western U.S., with only one new major fire reported in Wyoming yesterday. One large fire in Washington was contained yesterday, while other fires in Washington and California are nearing containment.

Some lightning caused fires are considered to be beneficial for the restoration of wilderness areas, and are being allowed to burn themselves out naturally.

NCAR is managed by the University Corporation for Atmospheric Research, a consortium of 66 universities offering PhDs in atmospheric and related sciences.